bug#70727: cp doesn't recognize the new --update=none-fail option

[Attila Fidan]

Hi,

I wanted to use the new cp --update=none-fail option introduced in 9.5,
but it said "invalid argument ‘none-fail’ for ‘--update’". It turns out
that the commit (49912bac286eb3c0ef7d1567ae790193ad5eb2e8) adding it
forgot to add the new operation to update_type[] and
update_type_string[] in cp.c like it did for mv.c. After patching
coreutils locally the functionality works as expected.

It seems like the test suite didn't catch this because there's no
cp/update.sh test like there is for mv. There's a test for if using
--backup and --update=none-fail are mutually exclusive by checking if cp
returns 1, but an invalid argument also makes cp return 1 :)

I didn't include a patch in case a change to the test suite is wanted,
but the proposed change is tiny and rather obvious.

Thanks!